Despite 20 years of unprecedented growth in the number of criminal justice-involved older adults (those under arrest, in court, in prison or jail, on probation or parole), the knowledge needed to develop evidence-based interventions for this population with high rates of early onset disease, disability and behavioral and social risk factors, is deeply under- developed. In particular, research to understand the life course experiences, the social determinants of health, and the drivers of later life health disparities in this population, including criminal justice involvement itself, is limited. Moreover, much of the research about this population has failed to study geriatric conditions (e.g., functional and cognitive impairment, falls, elder abuse, polypharmacy) that are key to understanding the health and wellbeing of older adults at each phase of criminal justice involvement (from arrest through community reintegration after incarceration). This lack of knowledge has profound impacts on public health as over 95% of incarcerated patients are eventually released to the community where they disproportionately rely on community safety net healthcare systems. The relative lack of evidence in this area of aging and health disparities research reflects, in part, professional isolation among the growing number of researchers who study aging and criminal justice involvement ? many of them early in their careers ? from a range of academic disciplines (e.g. medicine, public health, nursing, epidemiology, social welfare) spread throughout the nation with few centered at any one institution. As a result, vital interdisciplinary research collaborations are limited and junior researchers often lack the mentorship needed to pursue a successful research career in this area. In response, we propose developing The ARCH (Aging Research in Criminal justice & Health) Network to build research capacity in this emerging field and catalyze the impactful research needed to develop evidence-based interventions that meet the needs of this historically overlooked population of older adults. To meet these goals, we propose two specific aims: (1) to establish a multidisciplinary national research network to develop and refine the research agenda, measures, and methods needed to advance research on the health and social drivers of criminal justice involvement and health disparities among older adults over the life course and the consequences of criminal justice involvement on health in later life; and (2) to support new and established scientists to develop and implement life course research on the health of criminal justice-involved older adults by offering a research technical assistance program, creating a national mentorship program for junior investigators, directly funding pilot and exploratory research, and creating formal opportunities for networking to develop new multidisciplinary research collaborations. The ARCH Network will ensure that geriatric principles are front and center in studying the health and healthcare needs of criminal justice-involved older adults and will develop a research agenda that can inform correctional and community healthcare systems of opportunities across the life course where programmatic and policy interventions can be tested to reduce health disparities for this population.